– Angiotensin converting enzyme inhibitors (ACE inhibitors) are drugs that block the body’s production of angiotensin II. Angiotensin II is a hormone that circulates in the blood and has many effects on the cardiovascular system; its main role is to constrict blood vessels. This constriction can cause high blood pressure and increase the work required for the heart to pump blood into the body’s main arteries. This causes a problem for the heart muscle if it has been weakened by a heart attack or heart failure. Blocking production of angiotensin II with ACE inhibitors prevents constriction of blood vessels, lowers blood pressure, and lessens the energy the heart has to expend from beat to beat.

β blockers (Metoprolol, Atenolol, Bisoprolol, Propranolol)

– Beta-blockers lower your blood pressure by blocking the effect of hormones called adrenaline and ­noradrenaline. By blocking these hormones, beta-blockers slow down your heart rate and reduce the force at which blood is pumped round your body.

Beta-blockers also block your kidneys from ­producing a hormone called angiotensin II. Reducing the amount of angiotensin in your body allows your blood vessels to relax and widen, making it easier for blood to flow through.

Angiotensin receptor blockers (Telmisartan, Losartán, Olmesartán)

Angiotensin II is a natural substance in your body that affects your cardiovascular system in many ways, such as by narrowing your blood vessels. This narrowing can increase your blood pressure and force your heart to work harder. Angiotensin II also starts the release of a hormone that increases the amount of sodium and water in your body, which can lead to increased blood pressure. Angiotensin II can also thicken and stiffen the walls of your blood vessels and heart.

Centrally acting agents:

α2-Agonists (Methyldopa, Clonidine)

– Alpha-adrenergic receptors play an important role in the regulation of blood pressure (BP). There are 2 principal types of alpha receptors, alpha 1 and alpha 2, and both participate in circulatory control. Alpha 1 receptors are the classic postsynaptic alpha receptors and are found on vascular smooth muscle. They determine both arteriolar resistance and venous capacitance, and thus BP. Alpha 2 receptors are found both in the brain and in the periphery. In the brain stem, they modulate sympathetic outflow. Their function in the periphery is not yet fully understood, but they may contribute both to control of sympathetic tone and to local and regional blood flow. Drugs that enhance central alpha 2 activity, such as clonidine, guanfacine and the active metabolite of methyldopa, can significantly lower BP and are effective in the long-term control of hypertension, either alone or in combination with other drugs.

α-Blockers (Prazosin,Terazosin)

– Alpha blockers relax certain muscles and help small blood vessels remain open. They work by keeping the hormone norepinephrine (noradrenaline) from tightening the muscles in the walls of smaller arteries and veins. Blocking that effect causes the vessels to remain open and relaxed. This improves blood flow and lowers blood pressure.

Because alpha blockers also relax other muscles throughout the body, these medications can help improve urine flow in older men with prostate problems.

When blood vessels dilate, the flow of blood is increased due to a decrease in vascular resistance. Therefore, dilation of arterial blood vessels (mainly the arterioles) decreases blood pressure. The response may be intrinsic (due to local processes in the surrounding tissue) or extrinsic (due to hormones or the nervous system). In addition, the response may be localized to a specific organ (depending on the metabolic needs of a particular tissue, as during strenuous exercise), or it may be systemic (seen throughout the entire systemic circulation).